Automatic multichannel selection



Oct. 27, 1953 o. F. HOTH ETAL' AUTOMATIC MULTICHANNEL SELECTION 10Sheets-Sheet 1 Filed Nov. 4, 1950 I INVNTOA S= ATTORNEY Oct. 27, 1953Filed Nov. 4, 1950 D. F. HOTH EF'AL AUTOMATIC MULTICHANNEL SELECTION I10 Sheets-Sheet 2 0. E Ham WVENTOPS R. 0. sorra BUM ATTORNEY Oct. 27,1953 D. F. HOTH EI'AL 2,657,266

AUTOMATIC MULTICHANNEL SELECTION Filed NOV. 4, 1950 10 Sheets-Sheet 3 REC CARR/ER OPR DEV/CE T DLQ IDLE ' TONE .0. fff/OTH IAIVENTOA S- R Lay/Md FIG. 3

D. F. HOTH ET AL AUTOMATIC MULTICHANNEL SELECTION 10 Sheets-Sheet 4Filed Nov. 4, 1950 DQl-THOTH WVENTOPS' R. 0. SOFFEL By ATTORNEY Oct. 27,1953 D. F. HOTH 'EIAL 2,657,266

AUTOMATIC MULTICHANNEL SELECTION Filed Nov. 4, 1950 6 1O Sheets-Sheet 5.0. EHOTH R. 0. sorra ATTOIPNEV FIG. .5

Oct. 27, 1953 D. F. HOTH ETAL AUTOMATIC MULTICHANNEL SELECTION FiledNov. 4, 1950 10 Sheets-Sheet 6 '0. E Ham R. 0. SOFFEL Oct. 27, 1953 D.F. HOTH ETAL 2,557,266

AUTOMATIC MULTICHANNEL SELECTION Filed Nov. 4, 1950 10 Sheets-Sheet 7ATTORNEY Oct. 27, 1953 D. F. HOTH ETAL 2,657,265

AUTOMATIC MULTICHANNEL SELECTION Filed Nov. 4, 1950 1o Sheets-Sheet 8 MV O M .0. E H0771 INVENTOPS. R Q SOFFEL ATTORNEY FIG. 8

Oct. 27, 1953 D. F. HOTH ETAL AUTOMATIC MULTICHANNEL SELECTION FiledNov. 4, 1950 10 Sheets-Sheet 9 #5 mwbt T 3 E v Q2 wm QQRUMKMQ MQQL Mu m820E EM MQQQE .0.- f. HOTH V R. 0. SOFFEL ,BVJ

ATTORNEV Oct. 27, 1953 D. F. HOTH ET'AL AUTOMATIC MULTICHANNEL SELECTION10 Sheets-Sheet 10 Filed Nov. 4, 1950 at Nat TuITui GE GE GE atnvvnvroes 5 RQSOFFEL B! j ATTORNEY Patented Oct. 27, 1953 UNITED STAATENT OFFICE Soflel, Hastings-on-Hudson, N. Y., assignors to BellTelephone Laboratories, Incorporated, New York, N. Y., a corporation ofNew York Application November 4, 1950, Serial No. 194,162

3 Claims.

This invention relates to telephone systems and especially to amultichannel common medium transmission system between a central or basestation and a plurality of outlying stations.

An object of the invention is to enable any one of a large num er ofoutlying stations to be selectively signaled from a central callingstation and be directed to connect itself to a particular one of aplurality of transmission channels, and to deny all other stationsaccess to this channel.

Another object of the invention is to enable any one of a large numberof outlying stations to establish a connection to the base station overany idle one of a plurality of transmission channels, and to cause allother stations to be denied access to this channel.

though this invention may be employed in other communication orsignaling systems, the embodiment in which it is here described is amultichannel mobile radio telephone system. As specifically applied tosuch a system, one of the objects is to provide a greatly improved gradeof service to mobile radio subscribers. Heretofore, mobile radio systemshave operated on the same principle as a conventional party linetelephone system except that the number of subscribers in a mobile radiotelephone system greatly exceeds the number of parties that wouldordinarily be put on one conventional telephone 4 line. By providingeach mobile radio telephone subscriber with access to a plurality ofsignaling channels, the grade of service thus obtained is much betterthan that which would be obtained by dividing the number of mobilesubscribers in smaller groups and assigning each group to one channelonly. Furthermore, a larger number of mobile subscribers can beaccommodated by a multichannel system where all mobile subscribers haveaccess to all channels than by a system having several exclusivechannels.

Another object of the invention is to provide privacy for the mobilesubscribers by denying access of other subscribers to busy channels.

In this specification a transmission channel will be understood tocomprise two carrier frequencies, one for transmission in one directionand the other for transmission in the opposite direction. At the basestation a separate fixedtuned transmitter and receiver are provided foreach channel. Each mobile station is provided with a tunable transmitterand receiver.

In the system according to this invention the base station transmitsover some one of the channels that happen to be idle a modulation ofdistinctive frequency, hereinafter called the idle tone. Each mobilereceiver is equip ed with a hunting device which causes the receiver, inthe standby condition, to be tuned to the frequency of the channelcarrying idle tone. Should this channel become busy, idle tone isremoved and transferred to the next succeeding idle channel, causing allidle mobile stations to be tuned to the new channel.

Although for the purpose of the invention any system of selectivesignaling may be employed, the method herein described consists of thesimultaneous transmission of a combination of four audio frequencies,each mobile station being assigned an exclusive combination, asdescribed in the copending applications of H. C.

Harrison, Serial No. 767,487, filed August 8, 1947,

and D. F. I-Ioth-R. O. Soffel, No. 56,186, filed October 23, 1948.

nel;

Fig. 5 shows the system of'relays and circuits comprising the channelselector;

Figs. 6, '7 and 8 represent respectively a dial pulse counting circuit,a steering and lock circult, and a register and translator circuit;

Fig. 9 represents the units of a typical mobile station;

Fig. 10' is a block diagram for the entire system; and

Fig. 11 shows the order in which the preceding Figs. 1 to 8 are to beread.

The general operation of the invention will first be explained in termsof the block diagram shown in Fig. 10. Referring to this figure, a calloriginating from the base station will first be described. For thepurpose of this description it will be assumed that no channels are busyand that channel I is designated the idle channel, that is, the channelwhich is carrying idle tone. When an operator desires to originate acall, she inserts the plug of a cord circuit into a jack in the trunkcircuit shown as block l By means of a dial or any of the otherwell-known methods, the operator causes the number of the wanted stationto be registered in the register represented by block 2. When thecomplete number has been registered, the trunk transmits a signal overlead IOOI to the trunk selector, shown as block 3. The trunl; selectoroperates the select magnet corresponding to trunk I, on the crossbarswitch represented b block I2, over lead I004. When the select magnethas operated, it returns a signal over lead IfiiiS to the trunk selectorwhich then causes the channel selector shown in block 4 to operate thevertical hold magnet corresponding to the idle channel, in this casechannel I, over lead iEiIG. The operation or" the hold magnet causes agroup of contacts, in this case those designated Hl-Vi, to close andthereby pros vide a transmission path from the trunk I circuitrepresented by block 5 over lead group I003, through the operated switchcontacts to the channel I circuit represented by block 5 over lead groupi588. Previous to the operation of the hold magnet, a circuit was closedover lead I091 to remove the idle tone from the channel I transmitterrepresented by block 6. After the connection has been establishedbetween trunk I and channel l, the combination of four frequencies istransmitted from the register 2, through the trunk I, and through thecrossbar switch I2 to the transmitter 6 for channel I.

The hunting mechanism in the mobile receiver is slow to start in ordernot to allow the receiver to become tuned to another channel during theinterval between the removal of idle tone and the application of thesignaling tones at the base station. The mobile receiver which is beingsignaled, represented by block Iii, becomes locked to channel I by meansof the control circuit Ii, first by the ringing tones and then byswitchhook contacts when the mobile subscriber answers. At the end ofthe above-mentioned interval all other mobile receivers removethemselves from this channel and hunt for the new idle channel. When theconnection is established between trunk l and channel I, a circuit isenabled in the channel selector t to select the next succeeding idlechannel, in this case channel 2, and cause it to radiate idle tone. Whenthe connection thus established is terminated, channel I again becomesidle, but channel 2 remains the designated. idle channel.

When a mobile station originates a call, the reception of carrier fromits transmitter 9 by the fixed station receiver I causes the latterscodan to operate, which immediately causes idle tone to be removed fromthat channel. A signal is then sent over lead 56 I ii through thechannel I circuit represented by block 5 to the channel selector 4 overlead i905, indicating that a mobile station is originating a call. Thechannel selector signals the trunk selector 3 over lead IBIS to selectan idle trunk. The trunk selector then operates a horizontal selectmagnet corresponding to the idle trunk selected and signals the channelselector over lead HHS that this has been done. The channel selectorthen operates the vertical hold magnet associated with the properchannel, causing a connection to be established between the channel andtrunk circuits. The channel selector also selects the next succeedingidle channel and causes it to radiate idle tone.

In order to reduce the possibility of double connections which mightoccur during the interval irom the time of removal of idle tone from agiven channel (say channel l) until the mobile receivers have recognizedthe absence of this tone, the base station is so arranged that after ithas removed idle tone on a base station originating call it waits for apredetermined interval, designated the test interval, before setting upthe connection for signaling tones. This test interval, to whichreferences will be made hereinafter, includes the recognition time justmentioned plus the time that would be required for the base station torecognize waves starting from a mobile station just before the end ofthe latters recognition time. If a mobile call should originate and berecognized at the base station during this interval, the channel inquestion (channel I) is reserved for this call. However, the mobileoriginating call is halted temporarily and a reorder signal is sent tothe channel selector. The channel selector is then caused to select anew channel (say channel 2) for the base station originating call and toestablish this connection, after which the mobile originating call isallowed to proceed (over channel I). Should the above occur when onlyone channel is idle, the mobile call is halted as before and the trunkover which the base station call is being attempted is connected to theoverflow circuit represented by block 8. This circuit thereupon causesthe operators supervisory lamp to flash, thus indicating that there areno channels available to complete the operators call, there being onlyas many trunks as channels. The operator then removes the plug of hercord circuit from the trunk circuit jack and the mobile originating callproceeds over this abandoned trunk.

A detailed description of the invention will now be presented. As shownon the attached figures, a system having three trunks and three channelswill be described, in which any trunk may be connected to any channel.It will be evident to those skilled in the art that this system canreadily be expanded to care for any number of trunks and channels. Inorder to cover all features of the system, the operation of the circuitsfor the following cases will be considered:

(1) An operator originates a call when no channels are busy and channeli is the designated idle channel, that is, the channel carrying idletone.

(2) A mobile subscriber originates a call on channel 2, channel I stillbeing busy.

(3) An operator originates a call on channel 3, but a mobile subscriberoriginates a call on this channel during the test interval, causing theoperator to be routed to overflow. All channels are now busy, and thereis no idle tone.

(4) The connection on channel 2 is disconnected, causing idle tone to beput on this channel, the other channels remaining busy.

(5) With no channels busy and channel l the designated idle channel, asin (l), the operator originates a call and a mobile subscriberoriginates a call during the test interval, causing the operator's callto be rerouted to channel 2. Channel 3 is then designated the idlechannel.

(6) The call on channel I is disconnected.

Channel 1 designated the idle channel when starting up When the systemis first put into use, or restored to use after a shutdown, channel I isautomatically designated the idle channel as follows. Referring to Fig.2, ground from the armature and contact (5 of the releasedselect-magnetoperated relay 2% is connected over lead 2N to Fig. 5,through the armature and contact 2 of the test channel relay 5!, throughthe armature and contact 2 of each of the idle channel auxiliary relays506, 5H and 520, through the armature and contact 6 of, theall-channels-busy relay 508, through the contact I I and armature ofidle channel 3 relay 52 I through the contact I2 and armature of each ofthe idle channel relays 5E3 and 507, over lead 5II to Fig. 4, throughthe armature and contact of No. 1 hold magnet 402, over lead I2 to Fig.5 through the armature and contact I of mobile start relay 505, andthrough the winding of idle channel auxiliary I relay 506 to battery,causing the latter relay to operate and lock. The operation of relay 500connects ground from its armature and contact 4 through the upperwinding of idle channel I relay 501 to battery, causing it to operate.The operation of relay 50'! connects ground from the armature andcontact 3 of the test channel relay 50I, through the armature andcontact 0 of relay 501, through the contact I and armature of relay 500,over lead 309 to Fig. 3, and through the winding of the idle tone relay302 to battery, causing this relay to operate.

Idle tone will then be connected to transmitter 304 (Fig. 3) over thefollowing path: from the idle tone oscillator 30I, through contact 2 andthe armature of the idle tone relay 302, through contact I and thearmature of the talk relay 303 to the transmitter 304, and returnthrough the armature and contact 4 of relay 303 and through the armatureand contact 3 of relay 302 to the idle tone oscillator 30I. In Fig. 5,the operate hold magnet relay 502 will be operated from ground on thearmature and contact 3 of relay 204 in Fig. 2, over lead 2 I 3, andthrough the winding of relay 502 to battery.

Mobile stations hunt for idle tone When a mobile station is first putinto operation, it hunts over each channel in turn until the channel onwhich idle tone is being transmitted by the base station is received.The hunting then stops and the mobile station remains tuned to thischannel. This operation will now be described in detail. Referring toFig. 9, assume that when the mobile station is put into operation it istuned to channel 3. Assume also that idle tone is being transmitted bythe base station on channel I. The hunting control relay 005 isunoperated. A path is established from ground through the armature andcontact I of the hunting control relay 905 to the winding of the motor006 and thence to battery. The motor runs, driving switches 90! and 900slowly in a clockwise direction. Switch 000 connects crystals 9H3, 909,etc. in turn to the mobile receiver 90L In the system being described,the mobile receiver is assumed to be of the common superheterodyne typein which the signal from a local oscillator is combined with theincoming signal to produce an intermediate frequency signal. By changingthe frequency of the local oscillator the receiver can be tuned to a newchannel. It is assumed that a crystal controlled local oscillator isused and that the frequency of the oscillator is changed by substitutinga new crystal tuned to a different frequency. Thus, as switch 900rotates, connecting each of the crystals in turn, the receiver is tunedto each of the channels in turn. However, any other suitable type ofreceiver may be used, if desired.

When the wiper of switch 000 reaches segment I, crystal M2 is connectedto the mobile receiver and channel I is received. Since idle tone isbeing transmitted by the base station on channel I, it is received bythe mobile receiver SM and transmitted to the idle tone detector 902. Inthe idle tone detector the signal is transmitted through the band-passfilter 9I3 and the rectifier 9I4 to the coil of the idle tone relay 903.The rectifier converts the idle tone alternating current to a directcurrent which operates the idle tone relay. The operation of the idletone relay closes a path from ground through its armature and contact Ito the coil of the control relay 004 and thence to battery, operatingthe control relay. Operation of this relay closes a path from groundthrough its contact I and armature to the coil of the hunting controlrelay 905 and thence to battery. Operation of the hunting control relayopens the path from ground through its armature and contact I to themotor and thence to battery, causing the motor to stop running. Themobile receiver thereupon remains tuned to channel I. All other mobilestations receiving idle tone will become tuned to channel I in the samemanner.

Base station originates a call on channel 1 In order to originate a callthe operator inserts the plug of her cord into the trunk jack I02 inFig. 1 for trunk I. The insertion of the plug into jack I02 connectsground from its contact I through its armature over lead I I8 to Fig. 2,and through the winding of the busy I relay 20I to battery, causing thisrelay to operate. When relay 20I operates, ground on its contact I isconnected through its armature over lead IIB to light the busy lamp I06(Fig. 1). The operator then operates the dial key I04 which connects thedial I05 over lead I2I to Fig. 6. The relays shown in Fig. 6 comprise adial pulse counting circuit, those in Fig. 'l a steering and lockcircuit, and those in Fig. 8 a register and translator circuit. Theoperation of Figs. 6, 7 and 8 is described in detail in theaforementioned copending application of D. F. I-Ioth-R. O. Soffel,Serial No. 461,186, and will not be further described here.

When the operator has completed dialing four digits the trunk start Irelay 202 (Fig. 2) is operated over the following path: from batterythrough contact 0 and armature of the unoperated relay 208, throughcontact 5 and armature of the unoperated relay 200, through the lowerwinding of relay 202, over lead II9 to Fig. 1, through the armature andcontact 2 of the unoperated release start relay I08, over lead 'IIiI toFig. 8 and then to Fig. 7, through the armature and top contact of theoperated thousands lock relay I04, through the top contact and armatureof the operated hundreds lock relay I05, over lead I03 to block 700which contains similar lock relays for the tens and units digits, backover lead "I02 and through Figs. 8 and 1 to Fig. 2, and through thearmature and contact 2 of the unoperated start mobile 1 x, ay 203 toground.

The operation of relay 202 connects ground from its armature and contactI over lead 209 to Fig. 4, and through the winding of No. 1 selectmagnet 30i to battery, causing it to operate. The operation of theselect magnet continues its operating ground through its contact I andarmature over lead 2 I0 through Fig. 1 to Fig. 2 and through the windingof the select magnet operated relay 204, causing the latter to operate.The operation of select magnet 005 prepares a mechanical path foroperating one of the sets of contacts associated with this selectmagnet.

The operation of relay 200 releases the idle channel auxiliary relay 500in Fig. 5, which had been held over the following path: ground throughthe armature and contact 6 of relay 204,

over lead 2 I 4 to Fig. 5, through the armature and contact 2 of relay50I, through the armature and contact 3 of relay 506, and through itswinding to battery. The operation of relay 204 operates relay 50I inFig. 5 over the following path: ground from the armature and contact 5of operated relay 204, through contact 8 and armature of the startmobile relay 203, over lead 2I5 to Fig. 5, through the winding of thetest channel relay 50I, through resistance 503 (since relay 502 isoperated as previously described), through the armature and contact 5 ofthe operated idle channel I relay 501, over lead 5I0 to Fig. 4, andthrough the winding of No. 1 hold magnet 402 to battery. The hold magnet402 is marginal so that it will not operate under this condition becauseresistance 503 (Fig. 5) limits the current. Relay 50I, however, is asensitive relay and operates on this reduced current.

The release of the idle channel auxiliary relay 506 previously mentionedcauses the release of the idle tone relay 302 in Fig. 3 which had beenheld over the following path: ground from the armature and contact 3 ofrelay 50 I, through the armature and contact Ii of relay 501, throughcontact I and armature of relay 506, and over lead 300 to the idle tonerelay 302. The release of relay 302 opens the previously described pathconnecting the idle tone oscillator 30I to the transmitter 304.

When the test channel relay 50! in Fig. 5 cperates, it opens the lockingcircuit for the operate-holcl-magnet relay 502; but this relay is slowto release in order to provide the test interval previously described.When relay 502 releases it puts a short circuit across resistance 503through its armature and contact 3. This increases the current throughthe winding of hold magnet 402 sufiiciently to allow the latter tooperate. The operation of the hold magnet causes a set of contacts inFig. 4 designated I-II-VI to close. When these contacts close, thefollowing path is established between the transmitter 304 in Fig. 3 andthe hybrid coil H5 in Fig. 1 for the purpose of transmitting signalingtones over channel I from the transmitter 304, through the armature andcontact I of the unoperated relay 303, through the armature and contactI of the unoperated relay 302, over lead 3I2 to Fig. 4, through contact3 and armature of HI-VI, over lead I24 to Fig. 1, through winding I29 ofthe hybrid coil II5, over lead I25 to Fig. 4, through the armature andcontact 4 of HI-VI, over lead 3I3 to Fig. 3, through contact 4 andarmature of relay 302, and through contact 4 and armature of relay 303back to the transmitter 304. Hybrid coils II3, H4 and H5 in Fig. 1,together with amplifiers I through II2, are used to combine the foursignaling frequencies on leads 80I through 804 from the register andtranslator in Fig. 8, as described in the aforementioned copendingapplication of D. F. Hoth-R. O. Soffel, Serial No. 56,186.

When the contacts HI--VI close, a path is also established to operatethe sleeve I relay I01 in Fig. 1 as follows: battery through the windingof hold magnet 402, through its contact 2 and armature, through contactand armature of HI-VI over lead I23 to Fig. 1, through the winding ofrelay I07, and through the armature and contact I of the trunk jack I02to ground, allowing relay I01 to operate. The operation of relay I0Iconnects ground from its contact I and armature to supervisory lamp I03,causing it to light. This lamp indicates to the operator that theconnection 8- has been established to the idle channel and signalingtones transmitted, and that the mobile subscriber has not yet answered.

Relay I01 in Fig. 1 has a winding of comparatively low resistance andwhen it is connected in parallel with the winding of the test channelrelay 501 in Fig. 5 over the path previously described,- relay 50Ireleases. The release of relay 50I connects ground from its armature andcontact 5, through contact I and armature of relay 502, over lead 2 I8to Fig. 2, through the armature and contact 2 of relay 202, over leadI20 to Fig. 1, and through the winding of relay I08 to battery, causingthe latter relay to operate. When relay I08 operates it locks itselfthrough its contact I and armature to ground through the armature andcontact I of the trunk jack I02. The operation of relay I08 opens thepath to the trunk start I relay 202, causing it to release. The releaseof relay 202 removes ground from its contact I over leads 200 and H0thereby releasing magnet 40I in Fig. 4 and relay 204 in Fig. 2.

The release of relay 204 just mentioned connects ground from itsarmature and contact 3, over lead 2 I3 to Fig. 5, and through thewinding of the operate hold magnet relay 502 to battery, causing thelatter to operate, which is its normal condition.

The release of relay 204 also causes the operation of the idle channelauxiliary 2 relay 5H in Fig. 5 over the following path: ground from thearmature and contact 6 of relay 204, over lead 2I4 to Fig. 5, throughthe armature and contact 2 of relay 50 I, through the armature and.contact 2 of relays 506, 5I'I and 520, through the armature and contact3 of the operated relay 501, through the armature and contact I of theunoperated relay 5I8, over lead 522 to Fig. 4, through the armature andcontact 4 of the unoperated hold magnet 405, over lead 523 toFig. 5,through the armature and contact I of the mobile start relay 5I6, andthrough the winding of relay 5I'I to battery, causing the latter tooperate. When relay 5II operates it looks itself through its contact 3and armature, through contact 2 of relay 506, through contact 2 andarmature of relay 50I, over lead 2I4 to Fig. 2, and through contact 6and armature of relay 204 to ground. The operation of relay 5Il connectsground from its armature and contact 4 through the upper winding of theidle channel 2 relay 5I8 to battery, causing it to operate. Theoperation of relay 5IB opens the locking circuit for relay 501 which hadbeen previously established as follows: ground through the armature andcontact 9 of the unoperated relay 52I, through the armature and contactI0 of the then unoperated relay 5I8, through the armature and contact 9of the then operated relay 501, through contact 5 and armature of theunoperated relay 500, through the armature and contact I of relay 501,and through its lower winding to battery. The release of relay 50'!closes a locking path for relay 5I8 as follows: ground through thearmature and contact 9 of relay 52I, through the armature and contact 9of the operated relay 5I8, through the armature and contact 8 of theunoperated relay 501, through the contact 5 and armature of relay 508,through the armature and contact I of relay 5I8, and through its lowerwinding to battery.

The operation of the idle channel 2 relay 5I8 closes a path to operatethe idle tone relay 302 for channel 2 as follows: ground from thearmature and contact 3 of the unoperated relay 50I,

Response at called mobile station, channel 1 In th desired mobilestation, the circuits operate in the following manner. Referring to Fig.9, when idl tone is removed by the base station, the idle tone relay 003releases, opening the path from ground through its armature and contactI to the coil of the control relay 004 and thence to battery, causingthe control relay to release. Release of the control relay 904 opens thepath from ground through its contact I and armatur to the coil of thehunting control relay 905 and thence to battery. Th hunting controlrelay is slow releasing and remains operated for a short period, so thatthe tuning motor 906 does not start, but waits for the signaling tones.When the four signaling tones are transmitted by the base station, theyare received by the mobile receiver E and transmitted to the selector5H5. The selector operates in the manner described in the copendingapplication of D. F. Hoth-R. O. Soffel, Serial No. 56,186, operating theselector relay BIIl. Operation of the selector relay closes a path fromground through its armature and contact I to the bell 025 and thence tobattery, causing the bell to ring. A path is also established fromground through contact 2 of the operated selector relay IlIB- and itsarmature to the coil of the control relay 904 and thence to battery,causing the control relay to operate. The hunting control relay 00-5,since it is slow releasing, has not yet released. A path from groundthrough contact I and the armatur of the operated control relay 904 tothe coil of the hunting control relay 905 and thence to battery causesthe hunting control relay to remain operated, holding open the path fromground through the armature and contact I of the hunting control relayto the motor 906 and thence to battery. Thus the motor remains stopped.

When the subscriber answers he removes his handset en from theswitchhook 0I8, operating the switchhook contacts. A path is establishedfrom ground through contact 2 and the armature of the operated controlrelay 004, through the armature and contact I of the operatedswitchhoolr 0I0 and thence to the transmitter control circuit 920,causing the transmitter control circuit to activate the mobiletransmitter 9 I 9, which radiates carrier. The transmitter tuning switch90? is arranged to rotate in synchronism with the receiver tuning switch900 and connects crystals 02I92 i corresponding to the various channelsto the mobile transmitter, thus tuning the mobile transmitter to theproper channel. When the mobile transmitter is activated in the presentcase, crystal 924 is connected to the mobile transmitter and thus thetransmitter radiates on channel I. The telephon receiver 926 of thehandset 9I'I is connected to the mobile receiver by a' path through thearmature and contact 3 of the operated switchhook, through the armatureand contact 3 of the operated control relay 904, to the mobile receiver90I and back to the telephone receiver. The mobile set is now in thetalking condition. When the signaling tones are subsequently removed atthe base station, the selector relay .9; releases, opening the 10 pathfrom ground through its contact 2 and armature to the coil of thecontrol relay904 to battery. However, th control relay remains operatedby a path from ground through contact 2 and the armatur of the operatedswitchhook 9I8, through the armature and contact 0 of the control relay000, to the coil or the control relay and thence to battery. Release ofthe selector relay 0I0 opens the path from ground through its armatureand contact I to the bell 925 and thence to battery, causing the bell tostop ringing.

Response at other mobile stations The operation of each of the other(noncalled) mobile units when idle tone is removed at the base stationwill now be described. When idle tone is removed from channel I, it istransmitted on channel 2 as described previously. Removal of the idletone from channel I allows the operated idle tone relay 903 in all idlemobile stations to release. The path from ground through its armatureand contact I to the coil of the operated control relay 900 and thenceto battery is opened, allowing relay 900 to release. When signalingtones for the wanted station are transmitted on channel I by the basestation, the selector 0I5 in each of the other mobile units remainsunoperated and the selector relay M0 is therefore unoperated. Thus thecontrol relay 004 does not reoperate when the signaling tones arereceived. Release of the control relay 904 opens the path from groundthrough contact I and the armature of the control relay to the coil ofthe slow releasing hunting control relay 005 and thence to battery,allowing the hunting control relay to release after an interval (thisinterval being provided for a called station to recognize the signalingtones, as previously explained). A path is established from groundthrough the armature and contact I of the hunting control relay to themotor 000 and thence to battery, causing the motor to run. The motordrives switches 00? and 008 slowly in a clockwise direction, and afteran interval switch 008 connects crystal 9 in place of crystal 9I2 to themobile receiver QIlI. Thus channel 2 is received in place of channel I.Since idle tone is now being transmitted by the base station on channel2, it is received by the mobile receiver 00L This causes operation ofthe idle tone relay 903 as previously described. A path is establishedfrom ground through its armatur and contact I to the coil of the controlrelay 000 and thence to battery. The control relay again operates,establishing a path from ground through its contact I and armature tothe coil of the hunting control relay 005 and thence to battery,operating this relay. The path from ground through the armature andcontact I of relay 905 to the motor and thence to battery is opened andthe motor stops. The mobile station remains tuned to channel 2.

When idle tone is removed at the base station, the release of relays 003and 000 is not instantaneous, a finite time being required therefor. If,during this short interval, the operator at one of the non-calledstations should lift his handset 9I8 to initiate a call, his transmittercontrol 920 would be energized through contact I of the handset andcontact 2 of the not yet released relay 004, which would thereupon becomlooked through its contact 0 and contact 2 of the handset. This stationstransmitter would then be operating on channel I at the same time thatthe base station is transmitting on this channel. It is for the purposeof avoiding such a double 11 sqens on. ha re io y men oned e t intervalis provided at the base station, this be} ing. a brief delay between theremoval of idle tone and the application of the signaling tones, ef-

iectedfby th slow release. of relay 502. Circuits Response at basestation to answering mobile station When, the carrier is receivedfromthe answering mobile station by the receiver 395 in Fig. 3, itfcausesitscarrier operated device 3% to connec'tground through the winding of thesleeve relay Sillto battery, causing the latter to operate. Theoperation of relay 36? connects ground-from its armature and contact 2through the winding of, the t'alk relay to battery, causing the latterto operate. The operation of relay 3&3 disconmeets the signaling'tonesfrom the transmitter 3.0 4Jand connects the latter, to hybrid coil 363,through contacts 2 and 3 and associated armatures. 'Hybrid coil 36% isconnected over leads 3H1and 3 through contacts i and 2, respectively,and their associated armatures, of the con tact. roup Iii-Vi, over leads422 and E23, respectivelytoFig. 1 and to jack Hi2, thus establishingthetalking connection. When relay 3i)? operates it connectsground from itsarmature lead 3H1, through the armature and contact 5 of the contactgroup Hl-VI, and over lead 126, to Fig. 1 to the winding of relay Eli's,short-circuiting this relay and causing it to release, The release ofrelay it? extinguishes lamp I03; indicating to the operatorthat thecalled subseriber has answered. The operator now re leases the dial keyiiid in Fig. 1, causing the associated. register and translator circuitto be restored tonormal.

and Contact l over Mobile originating call on channel 2 A mobileoriginating call will now be described in detail. The station making thecall is tuned toichannel 2 andis receiving idle tone on that. channelfrom the base station, as previously described, channel I being busy.Referring to Fig. 9; the idle tone relay 903, the control relay 995i,and the hunting control relay 9&5 are operated and. the selector relay916 is unoperated. The motor 906 is stopped. When the subscriber origieates thecall he removes his handset 9!: from the switchhook 913,operating the switchhoolr c9ntacts. A path is established from groundthrough-contact 2 and the armature of theoperated control relay fiMthrough the armature and contact I of the operated switchhook dis, andto the transmitter control circuit 929, causing the mobile transmitter919 to be activated and radiate carrier on channel 2.

The telephonereceiver 926 of the handset 9|? isconnected to the mobilereceiver QGI through a path from the mobilereceiver through contact 3and thearmature of the operated control relay 904, through contact 3 andthe armature of the operated switchh0ok 9&8, thence to the telephonereceiver, and baek to the mobile receiver. The.

mobile set is now in the talking condition. When idle tone issubsequently removed from channel 2 at the base station, the idle tone,relay 9.031eleases, opening: the path from ground through its arma randcontact i. to the, coil of the. control relay 9M, and, thence tobattery. The control re.- lay remains operated, however, through a, pathfrom ground through contact 2 and the armature of the operatedswitchhook 918, through the armature and contact of the control relayto. the coil of the control relay, and thence, to battery. This holdsrelay 9%,. operated, and-thusholdsthe motor stopped.

When the carrier from the. mobile station. is received by the basestation receiver for channel 2, which is now the channel carrying, idletone, it enables its carrier operated device, 306 to operate the sleeverelay 36?. (it will be understood that Fig. 3.now represents basestationapparatus for. channel 2.) The operation of relay 39'? connectsground fromits armatureand contact Zthrough the Winding of talk relay303to battery, causing it to operate. The operation of relaytilt-removes. the idle tone oscillator from the, transmitter by openingcontacts i and a of relay 383 from their respective armatures.. Groundfrom the armature and contact i of relay 3D! is connected over. the lead3H. for channel 2. to Fig. 4, through the. armature and contact l of No.Zhold magnet 405, along conductor and through. the winding of, themobile start 2.1'eiay 5H5 to battery, causing it: to operate. When relay5l6. operates, ground. from its armature and contact 6, is connectedover lead 2H toFig. 2, through contact l and armature or" theunoperatedrelay 204, through the winding of the start mobile relay 283,- through--its armature and contact 6, through the armature; andcontact 5 of relay2&2, through the armature andcontact 5.01" relay. 265, and through thearmae ture and contact of relay 2B8to battery, causing the start mobilerelay 2031110 operate- When relay ZBBoperates, direct connectiontobattery is substituted for. the connection through the. above-mentionedcontacts of thev trunk start re-v lays 292, 286 and 298 by means of amake-before? break spring combination including contacts 5. and i5 andtheir associatedarmature of relay 203. Relay Zttloclzs itself throughits contact I and armature, over leadlii to Fig. 5, and through.

contact e .and armaturev of relay 515 to ground.

The operation of relay 2G3 connects ground.

through its contact through the armature and contact 2 of the operatedbusy I relay 201,

through the armature and contact 3 of the busy. 2- relay. 2st, andthrough the upper winding of the trunkstart 2 relay ZllBto battery,causing the; latter relay to operate. Locking ground is furnished torelay il lfiirom armature and contact 31 of relay 263, through armatureand contact 4..of

relay 205, and through its winding to battery.

The operation of relay 265' connects, ground from its armature andcontact over lead. 2i9to:

Fig. 4, through the winding of No.. 2 select mag.-

net 493 to battery, causing it to operate and con-. tinue its operatingground through its armatureand. contact 5 over lead 2 Hlto Fig. 2 andthrough.

the winding of .select-magnet-operated relay 204 to. battery, thuscausing this relay to operate:

The operation. of. relay 204. closes a path .from. ground through thearmature andv contact 1 -:of the. operated relay 2E3, through thearmature: and contact 4 of relay. 294, over lead 2 i l toFig. 5,.through the armature and contact 3 of the re.-.

leased, relay 519, throughthe armature and conetact 4 of..the mobilestart 2 relay 5l6; overv lead.-

523A to Fig. 4, and through the winding of No. 2 hold magnet 405 tobattery, causing it to operate and close contact group H2-V2. Whenmagnet 405 operates, ground is connected from the armature and contact Iof relay 307 in Fig. 3, over the lead 3 I4 for channel 2, and throughthe armature and contact 2 of magnet 405 to the winding to lock itoperated. The operation of magnet 405 removes ground from its contact I,causing the release of relay 5I6. The release of relay 5I6 removesground from its contact 6, allowing start mobile relay 203 to release.The release of relay 203 removes ground from its contact 4 which opensthe locking circuit of relay 200, allowing it to release.

When relay 204 in Fig. 2 operates as previously described, it removesground from its contact 6 over lead 2 It, thus opening a locking circuitfor the idle channel auxiliary 2 relay EII in Fig. 5, allowing it torelease. When the trunk start 2 relay 206 releases, it removes groundfrom its contact I over leads 2I and 2 I0 thereby allowing No. 2 selectmagnet 103 in Fig. 4 and the select magnet operated relay 204 in Fig. 2to release. The release of relay 204 connects ground from its armatureand contact 6 to lead 2% to Fig. 5, through the armature and contact 2of relay 50I through the armature and contact 2 of relays 506, 1 and520, through the armature and contact 3 of the operated idle channel 2relay SIB, through the armature and contact I of the idle channel 3relay 52I, over lead 524 to Fig. 4, through the armature and contact Iof the No. 3 hold magnet 200, along conductor 525, through the armatureand contact I of the mobile start 3 relay 5! 0, and through the windingof idle channel auxiliary 3 relay 520 to battery, causing the latterrelay to operate. Relay 520 is locked operated through its armature andcontact 3, through contact 2 and armature of relays 5II and 503, throughcontact 2 and armature of relay 50 I, over lead 2M to Fig. 2, andthrough contact 0 and armature of relay 204 to ground.

When relay 520 operates, ground is connected from its armature andcontact 4 through the upper winding of idle channel 3 relay 52I tobattery, causing it to operate. In operating, relay 32I opens thelocking path for the idle channel 2 relay 5I8 and provides a lockingpath for itself as follows: ground on the armature and contact 8 ofrelay 52L through the armature and contact 8 of released relay 5 I 8,through the armature and contact 3 of relay 501, through contact 5 andarmature of relay 503, through the armature and contact I of relay 52Land through its lower winding to battery. The operation of relay IIZIcloses a circuit from ground through the armature and contact 3 of thereleased relay 50I in Fig. 5, through the armature and contact 0 ofrelay 52I, through the contact I and armature of relay 520, over lead309 to Fig. 3 for channel 3, and through the winding of the idle tonerelay 302 to battery, causing it to operate and connect the idle toneoscillator 30! to the transmitter 304 for channel 3 as previouslydescribed for the other channels, thus making channel 3 the designatedidle channel. All idle mobile stations now move to channel 3 in themanner previously described.

When the contact group H2-V2 closes, ground from the armature andcontact I of the operated relay 307 in its associated Fig. 3 isconnected over the lead 3 I4 for channel 2 to Fig. 4, through thecontact 5 and armature of contact group H2-V2, over the lead I20 fortrunk 2 to its associated Fig. 1, through the winding of the sleeve Irelay I07, over the lead 8' for trunk 2 to Fig. 2, and through thewinding of the busy 2 relay 205 to battery, causing both relays I01 and205 to operate and the busy lamp I06 for channel 2 to be lighted, aspreviously described for channel I. Ground through the winding of relayI0'I in Fig. 1 for trunk 2 also is connected through the armature andnormally made contact 2 of jack I02 to call lamp IOI, causing it tolight. The operation of relay I01 connects ground from its contact I andarmature to light the supervisory lamp I03.

In order to acknowledge the call, the operator inserts the plug of thecord circuit into jack I02 for trunk 2. This causes ground from thecontact I and armature of jack I 02 to be connected to the lead M3 forchannel 2, which holds the busy 2 relay 205 in Fig. 2 operated andshort-circuits the winding of the sleeve relay I0! in Fig. 1, causing itto release. The release of relay I 01 extinguishes lamp I03. When theplug is inserted in jack I02, contact 2 of the jack is opened,extinguishing call lamp IOI. When contact group H2V2 in Fig. 4 isoperated, a path is closed through its contacts I and 2 and theirassociated armatures to connect the transmission path from trunk jackI02 in Fig. 1 to the hybrid coil 308 in Fig. 3 for channel 2, aspreviously described for channel I.

Base station originates a call on channel 3, and a. mobile calloriginates during test interval When the operator next desires tooriginate a call to a mobile station, channels I and 2 now being busy,she inserts the plug of her cord into the trunk jack I02 in Fig. 1 fortrunk 3, since this is-now the only idle trunk and is the one carryingidle tone, to which all idle mobile stations are tuned. The insertion ofthe plug in jack I02 causes ground to be connected from its contact Iover lead H8 for trunk 3 and through the winding of the busy 3 relay 201to battery, causing it to operate. The operation of this relay connectsground from its armature and contact I over lead H6 to Fig. 1 for trunk3 and to the busy lamp I03, causing it to light. As previouslydescribed, the operator registers the number to be called in theregister and translator circuit of Fig. 8. When the called number hasbeen registered, ground is connected from contact 2 and armature of theunoperated relay 203 in Fig. 2, through the armature and contact 3 ofrelays 202 and 200, over the lead 502" to the Fig. 7 associated withtrunk 3, through the contacts of the lock relays as previouslydescribed, back over lead IOI to Fig. 1, through contact 2 and armatureof the unoperated release start relay I08, over the lead IEO" for trunk3 to Fig. 2, and through the lower winding of the trunk start 3 relay208 to battery, causing it to operate.

The operation of relay 200 connects ground from its armature and contact2 over lead 220 to Fig. 4 and through the winding of No. 3 select magnet404 to battery, causing it to operate and to continue its operatingground through its contact I and armature over lead ZIEJ to Fig. 2 andthrough the winding of the select magnet operated relay 20-2 to battery,causing it to operate. The operation of relay 204 removes ground fromits contact 6, causing the release of the idle channel auxiliary 3 relay520 in Fig. 5. The release of relay 520 releases the idle tone relay 302in its associated Fig. 3, as previously described for other channels, inturn causing the removal of idle tone from its associated transmitter304.

When the select magnet operated relay 204 in .Fig. 2 operates, itconnects ground from its armature and contact 5, through contact 8 andarmature of the unoperated relay 253, over lead 2I5. to Fig. through thewinding of the test channel relay 50!, through resistance 553, throughthe armature and contact 5 of relays 551 and 5I8, through the armatureand contact 5 of the operated idle channel 5 relay 52l, over lead 525 toFig. t and, through the windin of the No. 3 hold magnet 405' to battery.Because of the series resistance'503 in Fig. 5, hold magnet: 405 doesnot get sufficient current to allow it cooperate, but relay 5M in Fig.5, being more sensitive, operateson this current. The operation of relay5i opens the locking circuit for theoperate hold magnet relay 552. Relay502, being-slow to release, does not release immediately this path isopened, its holding time being the previously defined test interval.

If'a. mobile subscriber now originates a call on channel 3 before hisreceiver has recognized the absence of .idle tone the circuits willoperate in the-following manner to give his call precedence overthat ofthe base station operator and thus prevent a double connection. The basestation receiver-305 in Fig. 3 for channel 3, on receiving the mobilecarrier, causes its carrier operated device 306 to operate the sleeverelay 551. The operation of relay 301 operates the talk relay 303aspreviously described, disconnecting the channel 3 transmitter 304 fromthe relay 352, through which idle tone or signaling tone is supplied,and connecting it to the hybrid coil 358 for speech. The operation ofrelay 351 also connects ground from its armature and contact l over lead3M", through the armature and contact I of holdmagnet 405 in Fig. 4,lead 52'! to Fig. 5, and through the winding of the mobile start 3 relayi5l9 to battery, causing it to operate. The operation of relay 5I9establishes the following path: ground on the armature and contact "1-of the operated idle channel 3 relay 52L through contact 5 and armatureof relay 5 l 8, over lead 2 I6 'to Fig. 2, through the armature andcontact 50f relay 203, through the armature and contact 2 of relay 204,over lead 212 to Fig. 5, and through the winding of the reorder rela 5%to battery, causing it to operate.

The operation of relay 595 reestablishes the locking circuit for relay502 over the following path: ground from the armature and contact l ofrelay 505', through the contact 2 and armature of relay 552, and throughthe winding of relay 502 to battery. The operation of relay 55-:connects ground from its armature and contact 2 through the armature andcontact 22 of relays 506, 5H and 520, through the armature and contact 3of relay 52I, through the armature and contact I of relay 501, over lead5H to Fig. 4, through the armature and contact 5 of hold magnet 402,over lead 5I3 to Fig. 5, through the armature. andcontact I of relay5I8, over lead 522 to Fig. 4, through the armature and contact 3 of holdmagnet 405, over lead 525 to Fig. 5, through the armature and contact 2of relay 521, and through the upper winding of the allchannels-busyrelay 508 to battery, causing it to operate. The'operation of relay 55%opens the locking circuit for the idle channel 5 relay 52l through thearmature and contact 5 of relay 5%, allowing relay 52 I to release.

, The release of relay 52I provides a locking circuit for relay 508 asfollows: ground from the armaturcand contact 9.0f rela 52 I, through thearmature and contact III of relays 5I8 and 507, through contact 4 andarmature of relay 503, and through its lower winding to battery. Therelease of relay 52! removes the ground from its contact I0, which waspart of the operating path for the reorder relay 504, allowing thelatter to release. The release of relay 52I also opens the operatingcircuit for the test channe1 relay 50l through the armature and contact5 of relay 52L The release of relay 505 removes the looking ground forrelay 502 from contact! of relay 504. However, the release of relay 5lllreestablishes a locking path for relay 502.

With all the idle channel relays 55?, 5I8 and MI released, a path isagain established to operate the test channel relay 55I as follows:ground from the armature and contact 5 of relay 2% in Fig. 2, throughcontact 8 and armature of relay 253, over lead 2 i5 to Fig. 5, throughthe winding of relay 55!, through the resistance 553, through thearmature and contact 4 of relays 501, 5I8 and 52!, through the armatureand contact 3 of the all-channels-busy relay 553, through contact I andarmature of the all-channels-busy auxiliary relay 559, over lead 5 l 5to Fig. 4, and through thewinding of No. 4 hold magnet 45? to battery.As in previous cases, the marginal hold magnet 45? does not operate atthis stage, but relay 5ill does. The operation of relay 5% removes thelocking path for the slow-releasing relay 552, and after an interval thelatter releases. The release of relay 552 short-circuits resistance 553through its armature and contact 3, permitting the current to increasesufficiently to allow hold magnet 55? in Fig. 4 to operate.

Since No. 3 select magnet 355 in Fig. i is operated at this time, theoperation of hold magnet it? causes contact group H3Vl to be closed.Hold magnet 55? is then locked operated over the following path: groundfrom contact I and armature of the trunk jack I02 in the associated Fig.1 for trunk 3, over lead I25" to Fig. 4, through the armature andcontact 5 of contact group H3--I-I4, through contact I and armature ofhold magnet 50?, and through its winding to battery. This locking groundis also connected over lead 5I5 to Fig. 5, through the armature andcontact I of relay 559, through contact 3 and armature of relay 558,through contact 5 and armature of relays 52!, 550 and 55?, through thearmature and contact 3 of relay 552, and to winding of relay 50Lshort-circuiting the latter relay and causing it to release.

The release of relay 5M connects ground from its armature and contact 5through contact I and armature of relay 552, over lead MS to Fig. 2,through the armature and contact l of the trunk start 3 relay 253, overlead l25 for trunk 3 to its associated Fig. l, and through the windingof the release start relay I58, causing it to operate and look throughits contact l and armature to ground on lead I [8. The operation ofrelay I08 in Fig. 1 opens the operating circuit for trunk start 3 relay258 in Fig. 2, allowing it to release.

The release of the test channel relay 55I in Fig. 5 connects ground fromits armature and contact I over lead 409 to Fig. 4, through the armatureand contact 2 of hold magnet 151, over lead All! to Fig. 5, throughcontact I and armature of the all-channels-busy relay 558, and throughthe winding of the all-ohannels-busy auxiliary relay 555 tobattery-causing it to operate. The operation of relay 509 looks itselfoperated from ground on its armature and contact l? 2, through contact Iand armature of relay 508, and through the winding of relay 589 tobattery. The operation of relay 5539 opens the operating path for holdmagnet 46?, but the latter remains locked operated as previouslydescribed.

The release of trunk start 3 relay 2% in Fig. 2 opens the operating pathfor No. 3 select magnet l-M in Fig. i and select magnet operated relay234 in Fig. 2, permitting them to release. The release of relay 2% inFig. 2 closes the following path: ground from the armature and contact 6of the mobile start 3 relay H9 in Fig. 5, over lead 2 I I to Fig. 2,through contact i and armature of relay 2%, through the winding of thestart mobile relay 233, through its armature and contact 3, through thearmature and contact 5 of relays 232 and 2%, and through the armatureand contact 4 of relay 268 to battery, causing relay 253 to operate andlock itself over its contact 5 under control of the mobile start 3 relay5i?) in Fig. 5. The release of relay 2% in Fig. 2 reestablishes theoperating path for relay 582 in Fig. 5 as follows: ground from thearmature and contact 3 of relay 2&4, over lead 2 E3 to Fig. 5, andthrough the winding of relay 532 to battery.

When the contact group H3-Vd in Fig. 4 is closed, an intermittent groundfrom contact I and armature of the interrupter M38 is connected throughcontact 4 and armature or contact group I-I3-V4 over lead IZ'I" fortrunk 3 to the associated Fig. l, causing the supervisory lamp 533 toflash in synchronism with the interrupter. The operator thereuponreleases the dial key i236, causing the release of the register andtranslator, and withdraws the plug from trunk jack E52. Removal of theplug causes the ground on its contact l to be removed from itsassociated armature, which releases the busy 3 relay 23'. in Fig. 2 andthe No. 4 hold magnet it? in Fig. i. The re lease of hold magnet ill!releases contact group lit-Vt. The release of busy 3 relay 29?extinguishes its associated busy lamp Hit in Fig. l.

The release of relay 2t! also closes the follow ing path: ground fromthe armature and contact 4 of the start mobile relay 253 in Fig. 2,through the armature and contact 2 of relays 23%, 295 and 28?, andthrough the upper winding of trunk start 3 relay 2% to battery, causingthe latter relay to operate and look over the following path: ground onthe armature and contact 3 of relay 233, through the armature andcontact 3 of relay 23%, and through its upper winding to battery. Theoperation of relay 2&8 operates No. 3 select magnet 43% in Fig. i andselect magnet operated relay 26 3 in Fig. 2, as previomly described. Theoperation of relay 2% closes the following path: ground from thearmature and contact 7 of relay 233, through the armature and contact ofrelay 2%, over lead 23? to Fig. 5, through the armature and contact l ofmobile start 3 relay 5I9, over lead 526 to Fig. i, and through thewinding of No. 3 hold magnet 235 to battery, causing it to operate. Theoperation of hold magnet 586 looks itself over the following path:ground from the armature and contact l of the sleeve relay 3371' in theassociated Fig. 3, over lead 3H3" for channel 3, through the armatureand contact 2 of hold magnet tilt, and through its winding to battery.The operation of hold magnet 166 in Fig. 4 also releases mobile start 3relay 5L9 in Fig. 5 by removing ground from contact I of hold magnet43%. Since No. 3 select magnet M34 in Fig. 4 is operated, the operationof hold magnet 438 operates the contact group H3V3. The release of relay5I9 in Fig.

i3 5 removes ground from the locking circuit of the start mobile relay263 in Fig. 2, allowing it to release.

The operation of contact group HS-VB in Fig. 4 closes the followingpath: ground from the armature and contact 5 of the sleeve relay 3%? inthe associated Fig. 3, over lead 3M" for channel 3 to Fig. 4, throughcontact 5 and armature of contact group H3V3, over lead I25 for trunk 3to the associated Fig. 1, through thewinding of the sleeve I relay till,and through the armature and contact 2 of trunk jack I02 to call lampWI. Closure of this path causes relay I07 to operate and also causescall lamp IEII to light. Ground through the winding of relay H3! is alsoconnected over lead H8" for trunk 3 to Fig. 2 and through the winding ofbusy 3 relay 201 to battery, causing it to operate. The operation ofrelay 23's connects ground from its armature and contact I over leadlit" for channel 3 to its associated Fig. 1 and to the busy lamp I36,causing it to light. The operation of relay ID! in Fig. 1 connectsground through its contact I and armature to the supervisory lamp H13,causing it to light.

When the call lamp IDI in Fig. 1 for trunk 3 lights, the operator againinserts the plug of her cord circuit into the associated trunk jack I02.This extinguishes the call lamp IBI by removing ground from contact 2 ofjack I02. Ground on contact i and armature of jack I02 is now connectedto lead H8", thus short-circuiting the winding of relay I97, causing itto release and also providing a path over lead H3 to Fig. 2 to hold thebusy 3 relay 207 operated. The release of the sleeve l relay I01 in Fig.l extinguishes the supervisory lamp I03. As previously described formobile originating calls, a talking path is now established from jackI02 in Fig. 1, through contact group H3-V3 in Fig. 4, and through hybridcoil 333 and talk relay 303 in Fig. 3 to the transmitter 304 andreceiver 335 for channel 3. At this point connections have beenestablished on all three channels and there is thus no idle channel.

All channels busy, no idle tone Since idle tone is now not received atany of the idle mobile units, their idle tone relays release. Referringto Fig. 9, release of the idle tone relay 903 in an idle mobile unitopens the path from ground through its armature and contact I to thecoil of the control relay 904 and thence to battery, causing the controlrelay to release. The path from ground through contact I and thearmature of the control relay 904 to the coil of the hunting controlrelay 905 and thence to battery is open, causing the hunting controlrelay to release after an interval. A path is established from groundthrough the armature and contact I of the unoperated hunting controlrelay 905 to the motor 906 and thence to battery, causing the motor torun. The motor drives switches and 908 slowly'in a clockwise direction,causing the crystals 3 I 0, 909, etc., to be connected in turn and themobile receiver 90! to be tuned to each channel in turn. Since no idletone is being transmitted on any channel, the mobile station continuesto hunt over the channels in turn.

If the mobile subscriber now attempts to call, he removes his handset 9|I from the switchhook M8. The control relay 904 is unoperated. The pathfrom ground through the contact 2 and armature of the control relay 904,through the armature and contact I of the operated switchhook 9l8, andto the transmitter control circuit 920 is open. Thus the transmittercontrol circuit does not activate the mobile radio transmitter 9 I 0 andcarrier cannot be radiated, The telephone receiver 325 of the handset9I'l is not connected to the mobile radio receiver because the path fromthe mobile receiver through the contact 3 and armature of the controlrelay 904, and through the contact 3 and armature of the operatedswitchhook 9 I 8 to the telephone receiver and back to the mobilereceiver is open.

Restoration of idle tone The procedure by which an idle channel is'reestablished and idle tone restored when one of the connections isterminated will now be described. For the purpose of illustration itwill be assumed that the operator breaks down the connection on channel2 by removing the plug from jack N2 in Fig. 1 (this figure nowrepresenting channel 2). The removal of the plug from jack I02 removesthe short-circuit from the sleeve I relay I03, allowing it to reoperateand connect ground from its contact I and armature to the supervisorylamp I03, the lighting of which indicates that the mobile subscriber hasnot yet disconnected.

When the mobile subscriber on channel 2 disconnects, he returns hishandset 9I'I to the switchhook 9H3, releasing the switchhook contacts.This opens the path which operates the transmitter control circuit 920,causing it to release and turn off the mobile transmitter 9I9. The pathfrom the telephone receiver 920 of the handset ell to the mobilereceiver is broken and the telephone receiver is disconnected from themobile receiver. The path from ground through contact 2 and the armatureof the switchhook' 9 I 8, through the armature and contact 4 of thecontrol relay 904, to the coil of the control relay and thence tobattery is opened, causing the control relay to release. The path fromground through contact I and the armature of relay 904 to the coil ofthe hunting control relay 905 and thence to battery is opened. Sincerelay 905' is slow-releasing, it does not release immediately. Shortlythereafter idle tone is returned to channel 2 by the base station, asdescribed in the following paragraph. This causes operationof the idletone relay 903, closing a path from ground through its armature andcontact I to the coil of the control relay 00-0 and thence to battery,operating the control relay. The pathv from ground through contact I andthe armature of the control relay to the coil of the hunting controlrelay 905 and thence to battery is reestablished, and the huntingcontrol relay remains operated. The mobile station remains tuned tochannel 2.

When the mobile subscriber disconnects, the removal of his carrierdisables the carrier operated device 305 in Fig. 3 for channel 2',permitting the associated sleeve relay 3 0! to release. The release ofrelay 301. removes ground from lead 350 to Fig. 4, releasing the sleeverelay I-0 I for channel 2 in the associated Fig. l, the busy 2 relay 205in Fig. 2, and No. 2 hold magnet 405 in Fig. 4. The release of thelatter releases contact group H2-V2. Ihe release of the busy 2 relay20E; extinguishes its associated busy lamp I00 in Fig. 1. The release ofhold magnet 405 establishes the following path: battery through thewinding of the idle channel auxiliary 2 relay 5H, through contact I andarmature of relay 5 I 6, over lead 523 to Fig. 4, through contact 4 andarmature of hold magnet 405, over lead 522 to Fig. 5, through contact Iand armature of idle channel 2 relay 5I8, over lead 5I3- to Fig. 4,

through contact 3 and armature of hold magnet 402, over lead 5H to Fig.5, through contact I and armature of the idle channel I relay 501, overlead 529 to Fig. 4, through contact 3 and armature of hold magnet 406,over lead 524 to Fig. 5, through contact 2 and armature of theallchannels-busy relay 500, through contact 2 and armature of relays520, 5I'I' and 505, through contact 2 and armature of the test channelrelay 50I, over lead 2 I0 to Fig. 2, and through contact 6 and armatureof relay 200 to ground, causing the idle channel auxiliary 2 relay 5 I lto operate. Operation of relay 5H connects ground from its armature andcontact 4 through the upper winding of the idle channel 2 relay M0 tobattery, causing it to operate and lock in a manner similar to thatpreviously described for other idle channel relays.

The operation of relay 5; closes the followin path: ground from thearmature and contact 3 of relay 50I, through the armature and contact 6of relay 5I8, through contact I and armature of relay 5I'I, over lead309 for channel 2 to its associated Fig. 3, and through the winding ofthe idle tone relay 302 to battery, causing it to operate. The operationof relay 302 connects the idle tone oscillator 30I to transmitter 304for channel 2, as previously described for other channels. The operationof relay 5E8 opens the locking circuit for the all-channels-bu'sy relay508, allowing it to release and in turn permitting the all-channelsbusyauxiliary relay 509 to release.

The idle mobile units which continued to hunt during the period whenidle tone was not being transmitted on any channel stop hunting whenidle tone has been restored to channel 2 and their tuning switches havecaused their receivers to be tuned to channel 2. The circuits in themobile units perform the same operations as in the case previouslydescribed in which a mobile unit, which had been shut ofi, is put intooperation.

Mobile call originates during test interval, no channels busy The casewill now be described in which an operator originates a call to a mobilestation when no channels are busy, channel I is the channel carryingidle tone, and a call from another mobile station originates on channelI during the test interval. Under these circumstances the operators callis routed to channel 2, idle tone is transferred to channel 3, and thecalling mobile subscriber is given priority on channel I, to avoid adouble connection.

Since channel I is the designated idle channel, the following relayswill be operated before the operator originates the call. In Fig. 3 theidle tone relay 302 will be operated and idle tone will be connected totransmitter 300 over the following path: from the idle tone oscillator30I, through contact 2 and armature of the idle tone relay 302, throughcontact I and armature of the talk relay 303, to the transmitter 304,and return through the armature and contact 0 of relay 303, through thearmature and contact 3 of relay 302, and to the idle tone oscillator 30I. In Fig. 5, the idle channel I relay 501, the idle channel auxiliary Irelay 506, and the operate hold magnet relay 502 will be operated.

In order to originate a call, the operator inserts the plug of her cordinto the trunk jack I02 for trunk I. The insertion of the plug into jackI02 connects ground from contact I through its armature over lead I I8to Fig. 2, and through the winding. of the busy I relay 20I to battery,

